This invention relates to electric motor control systems, and more particularly, to motor control systems for DC brushless synchronous motors.
A DC brushless motor typically includes windings on the stator, rotating permanent magnets and a position sensing arrangement for indicating the rotor position. The winding energization is generally controlled by solid state switches that are responsive to the position indications to energize the windings in the proper commutated sequence. Motor control is achieved by controlling the magnitude of the winding excitation current. Control can be open loop or can be closed loop to control velocity, position or torque.
Although prior servo control systems using brushless DC motors have been effective in many installations, there have been limitations to the range of control that could be achieved. The developments in robotics, machine tool drives and spindle drives require smooth control over a broad range of speed, require a high smooth torque at zero speed, and require significant torque at high speeds. An object of this invention is to provide a control system for a brushless DC motor that will meet these objectives.